Everything In Its Time (Time After Time Book 1) by Dee Davis

Years ago while vacationing in Scotland, Katherine St. Claire believed she’d found the love of her life. She shared a night of passion with a stranger, in a hotel castle called Duncreag. But come morning, her lover had disappeared. And she has spent the last eight years trying to convince herself it was all a dream...Living in the 15th century, Iain Mackintosh remains haunted by the memory of his greatest love. Eight years ago, she disappeared, leaving behind a cairngorm earring as the only evidence of her existence. Iain’s family wants him to stop pining for this fantasy woman and submit to a sensible marriage. But Katherine suddenly returns to him and reveals to him where—and when she’s from...